The present disclosure relates generally to medical methods and devices. More particularly, the present disclosure relates to methods and systems for accessing the cerebral arterial vasculature and establishing retrograde blood flow during the interventional treatment of acute ischemic stroke.
Acute ischemic stroke is the sudden blockage of adequate blood flow to a section of the brain, usually caused by thrombus lodging or forming in one of the blood vessels supplying the brain. If this blockage is not quickly resolved, the ischemia may lead to permanent neurologic deficit or death. The timeframe for effective treatment of stroke is within 3 hours for IV thrombolytic therapy and 6 hours for site-directed intra-arterial thrombolytic therapy or interventional recanalization of a blocked cerebral artery. Reperfusing the ischemic brain after this time period has no overall benefit to the patient, and may in fact cause harm due to the increased risk of intracranial hemorrhage from fibrinolytic use. Even within this time period, there is strong evidence that the shorter the time period between onset of symptoms and treatment, the better the results. Unfortunately, the ability to recognize symptoms, deliver patients to stroke treatment sites, and finally to treat these patients within this timeframe is rare. Despite treatment advances, stroke remains the third leading cause of death in the United States.
Endovascular treatment of acute stroke is comprised of either the intra-arterial administration of thrombolytic drugs such as recombinent tissue plasminogen activator (rtPA), or mechanical removal of the blockage, or often a combination of the two. As mentioned above, these interventional treatments must occur within hours of the onset of symptoms. Both IA thrombolytic therapy, and interventional thrombectomy involve accessing the blocked cerebral artery. Like IV thrombolytic therapy, IA thrombolytic therapy has the limitation in that it may take several hours of infusion to effectively dissolve the clot.
Mechanical therapies have involved either capturing and removing clot, dissolving the clot, or disrupting and suctioning the clot. The most widely used of these mechanical devices is the MERCI Retriever System (Concentric Medical, Redwood City, Calif.). This system uses a balloon guide catheter and a microcatheter to deliver a coiled retriever across the clot, and then during balloon occlusion and aspiration of the proximal vessel, pulling the retriever with the clot into the guide catheter. This device has had initially positive results as compared to thrombolytic therapy alone.
Other thrombectomy devices utilize expandable cages, baskets, or snares to capture and retrieve clot. A series of devices using active laser or ultrasound energy to break up the clot have also been utilized. Other active energy devices have been used in conjunction with intra-arterial thrombolytic infusion to accelerate the dissolution of the thrombus. Many of these devices are used in conjunction with aspiration to aid in the removal of the clot and reduce the risk of emboli. Frank suctioning of the clot has also been attempted using microcatheters and syringes, with mixed results. Devices which apply powered fluid vortices in combination with suction have been utilized to improve the efficacy of this method of thrombectomy. Finally, balloons and stents have been used to create a patent lumen through the clot when clot removal or dissolution was not possible.
Some Exemplary Issues with Current Technology
Interventions in the cerebral vasculature often have special access challenges. Most neurointerventional procedures use a transfemoral access to the carotid or vertebral artery and thence to the target cerebral artery. However, this access route is often tortuous and may contain stenosis plaque material in the aortic arch and carotid and brachiocephalic vessel origins, presenting a risk of embolic complications during the access portion of the procedure. In addition, the cerebral vessels are usually much narrower than coronary or other peripheral vasculature. In recent years, interventional devices such as wires, guide catheters, stents and balloon catheters, have all been scaled down and been made more flexible to better perform in the neurovascular anatomy. However, many neurointerventional procedures remain either more difficult or impossible because of device access challenges. In the setting of acute ischemic stroke where “time is brain,” these extra difficulties may have a significant clinical impact.
Another challenge of neurointerventions is the risk of cerebral emboli. During the effort to remove or dissolve clot blockages in the cerebral artery, there is a significant risk of thrombus fragmentation creating embolic particles which can migrate downstream and compromise cerebral perfusion, leading to neurologic events. In carotid artery stenting procedures CAS, embolic protection devices and systems are commonly used to reduce the risk of embolic material from entering the cerebral vasculature. The types of devices include intravascular filters, and reverse flow or static flow systems. Unfortunately, because of the small anatomy and access challenges as well as the need for rapid intervention, these embolic protection systems are not used in interventional treatment of acute ischemic stroke. Some of the current mechanical clot retrieval procedures use aspiration as a means to reduce the risk of emboli and facilitate the removal of the clot. For example, the MERCI Retrieval System recommends attaching a large syringe to the guide catheter, and then blocking the proximal artery and aspirating the guide catheter during pull back of the clot into the guide. However, this step requires a second operator, may require an interruption of aspiration if the syringe needs to be emptied and reattached, and does not control the rate or timing of aspiration. This control may be important in cases where there is some question of patient tolerance to reverse flow. Furthermore, there is no protection against embolic debris during the initial crossing of the clot with the microcatheter and deployment of the retrieval device.
Another limitation of current systems is the difficulty in aspirating from the target artery only. Guide catheters are usually placed proximally in the carotid, vertebral or basilar artery below the blocked artery. Aspiration on the guide catheter pulls flow not just from the target artery but from other arteries branching off from the proximal artery. This reduces the suction force on the target artery and furthermore may reduce the level of blood flow to other tissue beds.
One severe drawback to current acute stroke interventions is the amount of time required to achieve recanalization, either during to access of the blocked cerebral artery, or time required to remove the blockage. Recanalization, either through thrombolytic therapy, mechanical thrombectomy, or other means, often takes hours during which time brain tissue is deprived of adequate oxygen. During this period, there is a risk of permanent injury to the brain tissue. Means to shorten the procedure time, and/or to provide oxygen to the brain tissue during the procedure, would reduce this risk.